DTC 24

Code 24 "Vehicle Speed Sensor (VSS) Circuit:

Wiring Diagram - Vehicle Speed Sensor (VSS) Circuit:

CODE 24

VEHICLE SPEED SENSOR (VSS) CIRCUIT


Circuit Description:

NOTE: Disregard a Code 24 set when drive wheels are not turning.

The ECM applies and monitors 12 volts on CKT 437 to the vehicle speed sensor. The VSS alternately grounds and opens CKT 437, when drive wheels are turning. This pulsing action takes place about 2000 times per mile and the ECM will calculate vehicle speed based on the time between "pulses." "Scan" reading should closely match speedometer reading. A Code 24 will set if:.

Indicated vehicle speed is less than 5 mph

Engine speed between 1100 rpm and below 3200 rpm

More than 20% TPS

Not in park or neutral

The above conditions must be met for a time longer than 40 seconds.


Test Description: Numbers below refer to circled numbers on the diagnostic chart.

1. This test monitors the ECM voltage on CKT 437. With the wheels turning, the pulsing action will result in a varying voltage. The variation will be greater at low wheel speeds. The cruise control must be switched "OFF," since it will affect the test.

2. A voltage of less than 1 volt at the ECM connector, indicates that CKT 437 is shorted to ground. Disconnect CKT 437 at the vehicle speed sensor. If voltage now reads above 10 volts, the vehicle speed sensor is faulty. If the voltage remains less than 1 volt, then CKT 437 is grounded. If CKT 437 is OK, check for a faulty ECM connector or ECM.


3. A steady 8-12 volts at the ECM connector indicates CKT 437 is open or a faulty vehicle speed sensor.

4. This is a normal voltage condition and indicates a possible intermittent condition. See "Intermittents" in DIAGNOSIS BY SYMPTOM - NO TROUBLE CODE STORED.

5. This step will isolate whether the problem is in CKT 437 or the ECM.